The invention is concerned with semi-duplex FDMA mobile radio system comprising mobile exchanges, base stations and mobile radios and having a cellular configuration, each cell having one or more radio channels.
In semi-duplex FDMA mobile radio systems, it is usually impossible to interrupt a mobile radio during its transmitting permission and transmit signalling to the mobile radio as the mobile radio is not able to receive signalling during its transmission. This problem is solved in the same applicant's parallel application Method for digital semi-duplex transmission (FI 934230) by interrupting the transmission of the mobile radio at predetermined intervals and listening to reverse signalling transmitted by the base station. Reversing the direction of the radio parts of a semi-duplex mobile radio from transmission to reception before receiving and again from reception to transmission after signalling requires certain guard periods on both sides of the reverse signalling. Due to the regular frame structure of information to be transmitted, such guard periods are often used repeatedly, even though none of the transceivers is transmitting speech or data, that is, even when no reverse information is being transmitted. In practice, this means that the frame structure all the time contains idle time.